Liquid chromatographic-electrospray tandem mass spectrometric method for the determination of mebendazole and its hydrolysed and reduced metabolites in sheep muscle

A quantitative liquid chromatographic-electrospray tandem mass spectrometric method for the determination of mebendazole, its hydrolysed metabolite and its reduced metabolite in sheep muscle has been optimised, validated and applied in a depletion study of the mebendazole-derived residues from edible tissues of sheep after a single oral treatment with the commercial formulation Ovitelmin ®. The anthelmintic compounds were extracted with ethyl acetate after the sample mixture had been made alkaline. The liquid chromatographic separation was performed on a reversed phase C 18 column. Gradient elution with a mobile phase consisting of water containing 0.1% formic acid and acetonitrile was applied. Because of the detection by a very selective tandem quadrupole mass spectrometer in MS/MS mode after atmospheric pressure electrospray ionisation, the presented drug residue analysis method is very sensitive. The confirmatory method was validated according to the revised EU requirements. Most parameters were found to be conform proved to be with the criteria. The validation limit or the minimum required performance limit for sheep muscle tissue was set at 10 μg kg −1. The evaluated validation parameters were stability, specificity, recovery, precision (repeatability and within-laboratory reproducibility), analytical limits (decision limit and detection capability) and applicability. The decision limit values obtained for mebendazole, the hydrolysed and the reduced metabolite were 11, 12 and 13 μg kg −1, respectively. The detection capabilities for these substances were 13, 15 and 16 μg kg −1, respectively. In the depletion study, residues of mebendazole and its two metabolites could be measured in muscle, liver, kidney as well as back fat samples. After 1 day of excretion, the residue concentrations ranged from 21 to 7630 μg kg −1. The highest residue concentrations were found in the liver samples. Except for the back fat samples, the highest residue values were always measured for the reduced metabolite. This substance in liver and the hydrolysed metabolite in kidney was found for 14 days after administration.